SpaceX founder Elon Musk plans to build and launch a giant rocket that can take people to Mars.

However, the system might also be able to transport passengers anywhere on Earth in less than an hour.

An astronaut says such a trip would “not be for the faint of heart” and could trigger powerful nausea.

In late September, SpaceX founder Elon Musk debuted a new plan for colonizing Mars with 1 million people.

The centerpiece of Musk’s roughly 42-minute talk was the “Big F—ing Rocket,” or BFR. Musk hopes to launch the first 35-story BFR toward the red planet by 2022.

But the billionaire tech mogul also teased a bonus use for the BFR: flying people anywhere in the world in less than one hour.

“If we’re building this thing to go to the moon and Mars, then why not go to other places on Earth as well?” Musk said during his presentation at the International Astronautical Congress.

The BFR design has two main sections: a rocket and a spaceship. The 191-foot-tall rocket would push the spaceship into orbit around Earth, then the 157-foot-long spaceship would fly about 100 people to Mars.

Everything would run on liquid methane and oxygen. The BFR would land itself and be fully reusable — a scheme that could slash the cost of access to space thousandfold.

The BFR’s spaceship could fly more than 4.6 miles per second, according to SpaceX — over 12 times as fast as the supersonic Concorde jets of yesteryear.

At that speed, passengers could get from Los Angeles to New York in just 25 minutes, Bangkok to Dubai in 27 minutes, London to New York in 29 minutes, and Delhi to San Francisco in 40 minutes, said a video Musk showed. (Watch the full clip at the end of this story.)

To understand what it may feel like to ride on Musk’s giant spaceship, we asked Leroy Chiao, a former NASA astronaut.

What a BFR ride around the world would feel like

Chiao knows a thing or two about spaceflight — he has flown on three NASA space shuttles, as well as a Russian Soyuz spacecraft to the International Space Station, and he has lived nearly 230 days in space.

“What Elon Musk is describing would be a suborbital flight halfway around the world,” Chiao told Business Insider in an email.

Suborbital vehicles don’t orbit Earth. Instead, they make a fast and high arc through space and careen back toward the surface.

“Launch, insertion, and entry would be similar to a capsule spacecraft” — like the Soyuz — “with the difference being in the final phase of landing,” Chiao said. “During launch on a rocket with liquid engines … the liftoff is very smooth, and one really can’t feel it.”

SpaceX/YouTube

After the BFR (also called a first stage) runs out of fuel, the spaceship would separate from the rocket and fire its own engines. Chiao said this moment would feel “a bit dynamic,” describing the experience in terms of G-force, the equivalent of gravity at Earth’s surface multiplied by a certain amount.

“Ignition of the next stage engine(s) causes a momentary bump in G-force,” he said. “As you get to the last part of ascent, you feel some G’s come on through your chest, but it is not uncomfortable.”

When the spaceship’s engines cut off, though, Chiao said you’d become “instantly weightless” as you temporarily coasted through space.

“You feel like you are tumbling, as your balance system struggles to make sense of what is happening, and you are very dizzy,” he added. “You feel the fluid shift [in your body], kind of like laying heads-down on an incline, because there is no longer gravity pulling your body fluids down into your legs. All this can cause nausea.”

This feeling is familiar to anyone who has drifted over a hill on a roller coaster or flown on a parabolic “zero-gravity” flight — often referred to as a “vomit comet” ride because of the intense nausea the experience can trigger.

“As you start to re-enter the atmosphere, you would feel the G’s come on smoothly and start to build,” Chiao said.

As the spaceship nosed up and down to shed speed, he added, you’d at points feel about 5 G’s, which would make you feel roughly five times as heavy.

SpaceX/YouTube

As the spaceship sped toward the ground, its engines would fire to land it on a floating barge.

“You would both feel and hear” the engines, Chiao said. “As the thrust builds, you would feel the G’s come on again, and then at touchdown, you would feel a little bump.”

As exciting as such a trip might be — and the hours of aircraft flying it’d save — Chiao said it wouldn’t be for everyone.

“This would not be for the faint of heart, and it is difficult to see how this would be inexpensive,” he added. “But the one thing I’ve learned from observing Elon is not to count him out.”

Watch the full video of Musk’s “Earth to Earth” space-transportation concept: